Arrangement for avoiding eddy current losses in transfer switch and selector switch units with interposed gear drive



Aug. 6, 1968 Filed June 1, 1966 T s m "as 36 A A. BLEIBTREU ARRANGEMENT FOR AVOIDING EDDY CURRENT LOSSES IN TRANSFER SWITCH AND SELECTOR SWITCH UNITS WITH INTERPOSED GEAR DRIVE 2 Sheets-Sheet 1 mravroR Mxxa/Mm Mm M WWW R W 1968 A. BLEIBTREU 3,395,254

ARRANGEMENT FOR AVOIDING EDDY CURRENT LOSSES IN TRANSFER SWITC AND SELECTOR SWITCH UNITS WITH INTERPOSED GEAR DRIVE Filed June 1, 1966 2 Sheets-Sheet 2 WW 6km MK MIA/WW KM United States Patent f 3,396,254 ARRANGEMENT FOR AVOIDING EDDY CUR- RENT LOSSES IN TRANSFER SWITCH AND SELECTOR SWITCH UNITS WITH INTER- POSED GEAR DRIVE Alexander Bleibtreu, Regensburg, Germany, assignor to Maschiuenfabrik Rheinhauscn Gebruder Scheubeclr K.G., Regensburg, Germany Filed June 1, 1966, Ser. No. 554,436 Claims priority, application Germany, June 30, 1965, M 65,750 2 Claims. (Cl. 200-153) ABSTRACT OF THE DISCLOSURE Disclosed below is a single-phase transfer and selector switch unit for tapped regulating transformers of the socalled Jansen-type. The transfer switch is arranged above the selector switch and the Geneva gear drive for the latter is interposed between the former and the latter. The outgoing lead connected to the transfer switch and the two leads conductively connecting the selector witch and the transfer switch extend transversely across the aforementioned Geneva gear drive. When two of the aforementioned three leads are current-carryin g, their currents are of equal magnitude and opposite direction, and thus magnetic fields thereof mutually cancel each other, precluding eddy current losses.

This invention relates to load-tap changers for regulating transformers, and it relates more particularly to a type of load-tap changers which is known as J ansentype loadtap changers.

Load-tap changers include selector switches and transfer switches and drive means for operating these two kinds of switches. Selector switches serve the purpose of selecing any desired tap along a tapped transformer winding intended to be connected into an electric circuit. Selector switches are not required to interrupt current-carrying circuits, or to close on current-carrying circuits. These two tasks are assigned to, and performed by, the transfer switches, i.e. the latter perform all switching operations under load.

The taps of tapped transformer windings are conductively connected to the selector switches. The selector switches are, in turn, conductively connected to the transfer switches. The particular geometry of selector switches and of transfer switches depends largely upon whether it is intended to integrate polyphase switching means into one sing-1e unitary structure, or to resort to single-phase switches operating, as required, in single-phase circuits, or certain polyphase circuits as, for instance, three-phase circuits of delta connected transformers. This invention is concerned with single-phase switching.

A widely used and preferred design of a single-phase tap-changing means, or single-phase tap-changers, includes a selector switch arranged at a relatively low level, and a transfer switch operatively related to the selector switch and arranged at a level above the selector switch, and a gear drive for the selector switch interposed between the selector switch and the transfer switch, the selector switch, the transfer switch and the aforementioned gear drive for the former being integrated to form a unitary structure. The latter is placed into the tank of a tapped oil-insulated transformer with which it is intended to be operatively re lated, and submersed in the body of oil contained in that tank.

This invention relates more particularly to units of the aforementioned description, and it is a general object of this invention to provide improved units of this description.

3,396,254 Patented Aug. 6, 1968 ice Integrated single-phase units including a selector switch, a transfer switch superimposed upon the selector switch and a gear for driving the selector switch interposed between the selector switch .and the transfer switch require leads for connecting the selector switch and the transfer switch and an outgoing transfer switch lead. It is common practice in single-phase units comprising a selector switch, a transfer switch and selector switch driving gear to extend the two leads connecting the selector switch and the transfer switch transversely across the gear drive for operating the selector switch, and to extend the outgoing lead of the transfer switch across the housing of the latter.

I have found that the aforementioned arrangement of the three leads of the transfer switch results in the generation of eddy currents in the gear of the selector switch which may attain such a magnitude as to result in a very undesirable increase of the temperature of the body of oil in which the transformer is immersed.

It is, therefore, another object of this invention to provide selector switch and transfer switch units including a gear drive for the former interposed between the two switches which are not subject to the aforementioned drawbacks and limitations including excessive heat losses.

I have found that the gears for operating the selector switch, which gears are in the form of a pair of Geneva gears, operate in effect as short-circuited secondary windings of a transformer which is energized by one of the current-carrying leads which project transversely across the two parallel planes defined by the aforementioned pair of Geneva gears and operate, in effect, as a primary transformer winding. The eddy currents generated in this pair of gears may reach such a magnitude as to significantly reduce the overall efiiciency of the transformer with which the load-tap changer is associated.

It is, therefore, another object of this invention to provide integrated selector switch, transfer switch and selector-switch-opera-ting gear units wherein no eddy currents are generated in the selector-switch-operating Geneva gears, and which units have an overall efficiency which is substantially larger than that in comparable prior art units.

According to the present invention the magnetic field generated by the current flowing in one of the leads conductively connecting the selector switch and the transfer switch is cancelled by the magnetic field generated by the current flowing in the outgoing lead extending parallel to the current-carrying lead conductively connecting the selector switch and the transfer switch. The outgoing lead is carrying a current which is equal, but whose direction is opposite to that in the lead conductively connecting the selector switch and the transfer switch. To achieve this cancellation of magnetic fields leads conductively connecting the selector switch and the transfer switch and the aforementioned outgoing lead of the transfer switch extends transversely across the Geneva gear drive of the selector switch.

For a more complete understanding of the invention reference may be had to the following detailed description thereof taken in connection with the accompanying drawings wherein FIG. 1 is a diagrammatic vertical section of a unit comprising a selector switch, a transfer switch and a selectorswitch-gear-drive, this figure also showing the tapped winding of a transformer operatively related to the above switch unit;

FIG. 2 is a section along II-II of FIG. 1; and

FIG. 3 is a section along III-III of FIG. 1.

Referring now to the drawings, numeral 1 has been applied to generally indicate a transfer switch. The latter comprises four fixed contacts a, relatively movable contact means b and a pair of switching resistors or change-over resistors R. The head portion 2 of the transfer switch 1 includes a gear drive for pivoting the movable contact means selectively in clockwise direction and in counterclockwise direction. This gear drive will be described below more in detail. Transfer switch 1 is housed in a cylindrical housing 3 which supports at the upper end thereof the aforementioned head portion 2. Reference character 4 has been applied to generally indicate a selector switch arranged below transfer switch 1. The selector switch 4 includes a plurality of fixed contacts 37 and 38 of which each is conductively connected to a tap of a tapped transformer winding Tr. Winding Tr is provided with a plurality of taps of which two are designated by the reference characters A and B. Fixed contacts 37, 38 are arranged in coaxial patterns and supported by rods 39 of insulating material. Fixed contacts 37 are conductively connected to the odd numbered taps of winding Tr and fixed contacts 38 are conductively connected to the even numbered taps of winding Tr. Fixed contacts 37 and 38 are arranged in two different horizontal planes. All odd numbered taps of winding Tr are conductively connected to the fixed contacts 37 arranged in a circular pattern at a higher level and all even numbered taps of winding Tr are conductively connected to the fixed contacts 38 arranged in a circular pattern at a lower level. The upper fixed contact 37 and the lower fixed contacts 38 define a pair of concentric circles. The selector switch 4 further comprises a pair of anular contacts 35, 36 of which one is arranged at substantially the same level as the fixed contacts 37 conductively connected to odd numbered taps of winding Tr and the other is arranged at substantially the same level as the fixed contacts 38 conductively connected to the even numbered taps of winding Tr. Contacts 35, 36 are arranged on the outer surface of hollow insulating column 32 by which they are supported. The selector switch 4 further comprises a pair of contact bridges 5 and 6 of which the former is arranged at a higher level than the latter. The contact bridges 5 and 6 are pivotable about a vertical axis defined by the straight line interconnecting the centers of the aforementioned two circular groups of fixed contacts 37, 38. This axis is identical with the axis of hollow column 32. Contact bridge 5 when pivoted is capable of selectively conductively interconnecting each of the fixed contacts 37 connected to an odd numbered transformer tap with the upper annular contact 35. In a like fashion contact bridge 6 when pivoted is capable of selectively conductively interconnecting each of the fixed contacts 38 connected to an even numbered transformer tap with the lower annular contacts 36. The type of selector switches which has been shown in the drawing in a relatively diagrammatic fashion has been described in considerable detail and has been claimed in US. Patent 3,194,900 to Alexander Bleibtreu, issued July 13, 1965 for Modular Tap-Changing Selector Switch for Connecting Selectively Fixed Tap Contacts to a Transfer Switch, assigned to the same assignee as the present invention, and in US. Patent 3,233,049 to Alexander Bleibtreu, issued Feb. 1, 1966 for Integral Selector Switch and Transfer Switch Unit for Tapped Regulating Transformers, assigned to the same assignee as the present invention. Reference may be had to these two patents for additional information regarding the structural details of the selector switch 4 having no immediate bearing on the instant invention. Selector switch 4 may be arranged in a housing of insulating material not shown in the drawings.

Reference numeral 7 has been applied to generally indicate the Geneva gear drive for selector switch 4. The gear drive in head 2 operates a vertical shaft 8 which, in turn, operates the Geneva gear drive 7 for the selector switch 4. The lower end of shaft 8 supports a gear 11. Pin 11a projects axially from the upper surface of gear 11 and pin 11b projects axially from the lower surface of gear 11. Reference numeral 15 has been applied to indicate a ho]- low or tubular cylindrical bearing arranged in coaxial relation to the upper group and the lower group of fixed contacts 37, 38 of selector switch 4. Bearing 15 supports a pair of superimposed Geneva gears 9, 10 each for operating one of the aforementioned contact bridges 5 and 6. The pins 11a, 11b projecting from gear 11 engage alternately Geneva gears 9, 10, and thus pivot alternately contact bridges 5 and 6 about the axis of hollow column 32. This may be achieved by the intermediary of insulating rods 33 and 34, as described in considerable detail in the aforementioned US. Patent 3,194,900.

Reference numerals 12 and 13 have been applied to indicate the two leads conductively interconnecting the selector switch 4 and the transfer switch 1. These two leads are covered by appropriate insulating means and project transversely through Geneva gear drive 7, and more particularly through the central passage defined by vertical bearing 15 for Geneva gears 9, 10. Numeral 14 has been applied to indicate the outgoing lead of transfer switch 1. This lead is likewise covered with appropriate insulating means and projects transversely through Geneva gear drive 7 or, to be more specific, through the central passage defined by vertical bearing 15 or Geneva gears 99, 10.

In the position of the parts illustrated in the drawing the following current path is established: Tap A of winding Tr, one of the fixed contacts 37 on the upper level of selector switch 4, contact bridge 5, upper annular contact 35, lead 12, left fixed contact a of transfer switch 1, movable contact means b of transfer switch 1, lead 14, terminal Y. It will be apparent that the current in leads 12 and 14 is of the same magnitude, but of opposite direc tions. As a result, the magnetic fields established by the current in leads 12, 14 cancel each other. Consequently no eddy currents are induced in vertical bearing 15 and in Geneva gears 9 and 10.

A change from tap A to tap B involves a pivotal motion of the movable contact means b of transfer switch 1 in clockwise direction as seen in FIG. 1. As far as the instant invention is concerned, the consecutive steps involved in the tap-changing operation are of no consequence, except the last step establishing the following current path. Tap B of winding Tr, one of the fixed contacts 38 on the lower level of selector switch 4, contact bridge 6, lower annular contact 36, lead 13, right fixed contact a of transfer switch 1, lead 14, terminal Y. It will be apparent that the current in leads 13, 14 is of the same magnitude, but of opposite direction. As a result, the magnetic fields established by the current in leads 13, 14 cancel each other. Consequently no eddy currents are induced in vertical bearing 15 and in Geneva gears 9 and 10.

In the particular embodiment of the invention illustrated, the head portion 2 houses a spring motor 21 which may be Wound up by driving shaft 26 by means of gear transmission 25 and crank mechanism 14, 23. Transfer switch 1 is operated by spring motor 21 by the intermediary of operating shaft 22.

Reference numeral 31 has been applied to indicate the housing of selector-switch-driving-gear 7, and reference numeral 41 has been applied to indicate the base or bottom plate of selector switch 4. Hollow insulating column 32 establishes a mechanical tie between housing 31 and base plate or bottom plate 41. Contact supporting rods 39 of insulating material form a squirrel-cage-shaped structure coaxial with hollow insulating column 32. The tubular operating rods 33, 34 for contact bridges 5, 6 revolve around hollow column 32 whenever other taps of transformer winding Tr are selected. In the position of selector switch 4 shown in FIG. 1 but either of the two taps A and B can be selected. To select other taps contact bridges 5, 6 must be operated by Geneva gears 9, 10 and operating rods 33, 34.

While, in accordance with the patent statutes, I have disclosed the specific details of one embodiment of the invention, it is to be understood that these details are merely illustrative, and that many variations thereof may be made without departing from the spirit and scope of the invention. It is my desire, therefore, that the language of the accompanying claims shall be interpreted as broadly as possible, and that it be limited only as required by the prior state of the art.

I claim as my invention:

1. A single-phase transfer switch and selector switch unit for tapped regulating transformers comprising:

(a) a selector switch for selecting taps of a tapped transformer winding and including a plurality of fixed contacts to be connected to the taps of a transformer winding and movable contacts selectively cooperating with said plurality of fixed contacts and pivotable about a vertical geometrical axis;

(b) a transfer switch including switch-over resistors for effecting tap-changes under load arranged above said selector switch;

(c) a Geneva gear drive for operating said selector switch interposed between said selector switch and said transfer switch;

(d) a pair of tap leads conductively connecting said movable contacts of said selector switch and said transfer switch and extending from said selector switch transversely across said Geneva gear drive to said transfer switch; and

(e) an outgoing lead connected to said transfer switch and extending in the direction of said vertical geometrical axis of said selector switch and transversely across said Geneva gear drive for operating said selector switch.

2. A transfer switch and selector switch unit as specified in claim 1 wherein said Geneva gear drive for operating said selector switch includes a vertical hollow bearing supporting a pair of Geneva gears, and wherein said pair of tap leads and said outgoing lead project through the cylindrical passage defined by said hollow bearing.

References Cited UNITED STATES PATENTS 3,233,049 2/1966 Bleibtreu 20011 ROBERT K. SCHAEFER, Primary Examiner.

H. BURKS, Assistant Examiner. 

